(NaturalNews) One of the most commonly eaten vegetables may help protect the body against heavy metals, according to studies linking onion extracts to reduced damage from cadmium exposure.

Cadmium is a widespread and highly toxic heavy metal that the Centers for Disease Control and Prevention (CDC) lists seventh out of the 275 most hazardous substances. The metal has been shown to cause toxicity to organs, including the bones, kidneys, lungs and reproductive organs, and has also been linked to cardiovascular disease and cancer. Cadmium may also impair brain function. A study by researchers from Arizona State University, published in the journal Biological Trace Element Research, showed that high blood levels of cadmium were one of the single most predictive factors for autism severity.

Extract prevents organ damage

A recent study, published in the journal Pathophysiology, sought to uncover some of the mechanisms by which cadmium causes organ toxicity and to explore whether onion extract could hamper or mitigate those mechanisms. Researchers divided rats into three groups, assigning them to consume either a normal diet (control group), a normal diet plus cadmium-contaminated drinking water or a normal diet plus cadmium-contaminated water and onion extract.

Cadmium was administered as 0.3 mg/L of CdSO4 in a dosage of 1.5 ml/kg body weight. Onion extract was administered in a dose of 1 ml/100 g body weight.

The researchers found that cadmium-exposed rats had significantly higher levels of total cholesterol, triglycerides, LDL ("bad") cholesterol and serum albumin than control rats. They also had significantly lower blood levels of testosterone, protein and HDL ("good") cholesterol. These changes indicated damage to the liver and kidneys, and possibly also to the heart and reproductive organs.

Rats given both cadmium and onion extracts did not suffer liver and kidney damage-induced changes to their blood proteins and lipid profiles. In addition, the antioxidant effects of the extract protected them from cadmium-induced oxidative stress. Onion extract also reduced (but did not eliminate) cadmium-induced changes to urinary volume and renal clearance. It did not cause any change to testosterone levels, however.

The study "provided the first evidence of the therapeutic efficacy of [onion extract] against atherosclerotic conditions and organ toxicity in Cd-intoxicated rats via a mechanism independent of the circulating testosterone level," the researchers wrote.

Quercetin responsible?

Many of the health benefits of onions are being attributed to quercetin, a naturally occurring chemical in the flavonol family that is also found in apples, tea and wine. Quercetin is a powerful antioxidant and anti-inflammatory that has been linked to reductions in blood pressure and improvements in cardiovascular health.

Some researchers have questioned whether dietary quercetin can really provide these benefits, noting that the compound is quickly broken down in the stomach and intestines. But according to a study published in the journal Atheroscleroisis in 2008, quercetin's immediate metabolites have similar anti-inflammatory properties to the original chemical. This suggests that eating a diet high in quercetin would indeed provide the benefits suggested by studies on the isolated chemical.

Another study, conducted by researchers from Zhejiang University in China and published in the journal Anatomical Record in 2010, found that quercetin prevented premature sperm cell death in mice that had been exposed to cadmium. The flavonol appeared to protect sperm cells by reducing cadmium-induced oxidative damage, as well as by countering cadmium's effects on certain proteins that play a role in programmed cell death.

Quercetin has also been linked to reduced rates of pancreatic cancer, in a study published in the American Journal of Epidemiology. The researchers in that study found that quercetin and other flavonols reduced rates of pancreatic cancer by 25 percent in nonsmokers and by 50 percent in smokers.

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